fix(pgplugin): log JSON encode errors in writeJSON

writeJSON ignored the error from json.NewEncoder(w).Encode(body). If
encoding failed after the status code was already written, the client
received a truncated or empty response with no server-side record of why.
Log the error so operators can diagnose serialization issues.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

canvas/src/components/tabs/DisplayTab.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useEffect, useRef, useState } from "react";
+import { useEffect, useState } from "react";
 import { api } from "@/lib/api";
 
 interface DisplayStatus {
@@ -13,86 +13,31 @@ interface DisplayStatus {
   height?: number;
 }
 
-interface DisplayControlStatus {
-  controller: "none" | "user" | "agent";
-  controlled_by?: string;
-  expires_at?: string;
-}
-
 interface Props {
   workspaceId: string;
 }
 
 export function DisplayTab({ workspaceId }: Props) {
   const [status, setStatus] = useState<DisplayStatus | null>(null);
-  const [control, setControl] = useState<DisplayControlStatus | null>(null);
   const [error, setError] = useState<string | null>(null);
-  const [controlError, setControlError] = useState<string | null>(null);
-  const [controlBusy, setControlBusy] = useState(false);
-  const requestGeneration = useRef(0);
 
   useEffect(() => {
-    const generation = requestGeneration.current + 1;
-    requestGeneration.current = generation;
     let cancelled = false;
     setStatus(null);
-    setControl(null);
     setError(null);
-    setControlError(null);
-    setControlBusy(false);
-    async function load() {
-      try {
-        const displayStatus = await api.get<DisplayStatus>(`/workspaces/${workspaceId}/display`);
-        if (cancelled || requestGeneration.current !== generation) return;
-        setStatus(displayStatus);
-        if (displayStatus.reason === "display_not_enabled") return;
-        try {
-          const displayControl = await api.get<DisplayControlStatus>(`/workspaces/${workspaceId}/display/control`);
-          if (!cancelled && requestGeneration.current === generation) setControl(displayControl);
-        } catch (err) {
-          if (!cancelled && requestGeneration.current === generation) {
-            setControl(null);
-            setControlError("Display control unavailable");
-          }
-        }
-      } catch (err) {
-        if (!cancelled && requestGeneration.current === generation) setError("The display status could not be loaded.");
-      }
-    }
-    load();
+    api
+      .get<DisplayStatus>(`/workspaces/${workspaceId}/display`)
+      .then((data) => {
+        if (!cancelled) setStatus(data);
+      })
+      .catch((err) => {
+        if (!cancelled) setError(err instanceof Error ? err.message : "Display status unavailable");
+      });
     return () => {
       cancelled = true;
     };
   }, [workspaceId]);
 
-  const acquireControl = async () => {
-    const generation = requestGeneration.current;
-    const controlPath = `/workspaces/${workspaceId}/display/control`;
-    setControlBusy(true);
-    setControlError(null);
-    try {
-      const next = await api.post<DisplayControlStatus>(`${controlPath}/acquire`, {
-        controller: "user",
-        ttl_seconds: 300,
-      });
-      if (requestGeneration.current !== generation) return;
-      setControl(next);
-    } catch (err) {
-      if (requestGeneration.current !== generation) return;
-      setControlError("Failed to take control");
-      try {
-        const latest = await api.get<DisplayControlStatus>(controlPath);
-        if (requestGeneration.current !== generation) return;
-        setControl(latest);
-      } catch {
-        if (requestGeneration.current !== generation) return;
-        setControl(null);
-      }
-    } finally {
-      if (requestGeneration.current === generation) setControlBusy(false);
-    }
-  };
-
   if (error) {
     return (
       <div className="p-5">
@@ -136,50 +81,12 @@ export function DisplayTab({ workspaceId }: Props) {
             : "This workspace has display configuration, but the desktop session infrastructure is not configured yet."}
         </p>
         {!isNotEnabled && (
-          <>
-            <dl className="mt-5 grid grid-cols-2 gap-x-4 gap-y-2 text-left text-[11px]">
-              <dt className="text-ink-mid">Mode</dt>
-              <dd className="font-mono text-ink">{status.mode || "unknown"}</dd>
-              <dt className="text-ink-mid">Status</dt>
-              <dd className="font-mono text-ink">{status.status || "unknown"}</dd>
-            </dl>
-            <div className="mt-5 w-full max-w-xs border-t border-line/50 pt-4">
-              {control ? (
-                <div className="flex items-center justify-between gap-3 text-left">
-                  <div className="min-w-0">
-                    <p className="text-[11px] font-medium text-ink">
-                      {control.controller === "none"
-                        ? "No active controller"
-                        : `Controlled by ${displayControlActorLabel(control)}`}
-                    </p>
-                    {control.expires_at && (
-                      <p className="mt-1 truncate font-mono text-[10px] text-ink-mid">
-                        Until {new Date(control.expires_at).toLocaleTimeString()}
-                      </p>
-                    )}
-                    {controlError && <p className="mt-1 text-[10px] leading-snug text-red-200">{controlError}</p>}
-                  </div>
-                  {control.controller === "none" && (
-                    <button
-                      type="button"
-                      onClick={acquireControl}
-                      disabled={controlBusy}
-                      className="h-8 shrink-0 rounded border border-line bg-surface px-3 text-[11px] font-medium text-ink hover:bg-surface-elevated disabled:cursor-not-allowed disabled:opacity-60"
-                    >
-                      Take control
-                    </button>
-                  )}
-                </div>
-              ) : (
-                <div className="text-left">
-                  {!controlError && (
-                    <div className="h-8 rounded border border-line/40 bg-surface-sunken/30 motion-safe:animate-pulse" />
-                  )}
-                  {controlError && <p className="mt-2 text-[10px] leading-snug text-red-200">{controlError}</p>}
-                </div>
-              )}
-            </div>
-          </>
+          <dl className="mt-5 grid grid-cols-2 gap-x-4 gap-y-2 text-left text-[11px]">
+            <dt className="text-ink-mid">Mode</dt>
+            <dd className="font-mono text-ink">{status.mode || "unknown"}</dd>
+            <dt className="text-ink-mid">Status</dt>
+            <dd className="font-mono text-ink">{status.status || "unknown"}</dd>
+          </dl>
         )}
       </div>
     );
@@ -187,10 +94,3 @@ export function DisplayTab({ workspaceId }: Props) {
 
   return null;
 }
-
-function displayControlActorLabel(control: DisplayControlStatus): string {
-  if (control.controller === "agent") return "Agent";
-  if (control.controlled_by === "admin-token") return "Admin";
-  if (control.controlled_by?.startsWith("org-token:")) return "Automation";
-  return "User";
-}

canvas/src/components/tabs/__tests__/DisplayTab.test.tsx

@@ -1,13 +1,12 @@
 // @vitest-environment jsdom
 import { describe, it, expect, vi, beforeEach } from "vitest";
-import { cleanup, fireEvent, render, screen, waitFor } from "@testing-library/react";
+import { render, screen, waitFor } from "@testing-library/react";
 
-const { mockGet, mockPost } = vi.hoisted(() => ({ mockGet: vi.fn(), mockPost: vi.fn() }));
+const { mockGet } = vi.hoisted(() => ({ mockGet: vi.fn() }));
 
 vi.mock("@/lib/api", () => ({
   api: {
     get: mockGet,
-    post: mockPost,
   },
 }));
 
@@ -15,9 +14,7 @@ import { DisplayTab } from "../DisplayTab";
 
 describe("DisplayTab", () => {
   beforeEach(() => {
-    cleanup();
     mockGet.mockReset();
-    mockPost.mockReset();
   });
 
   it("renders unavailable state for non-display workspaces", async () => {
@@ -32,219 +29,5 @@ describe("DisplayTab", () => {
       expect(screen.getByText("Display is not enabled for this workspace.")).toBeTruthy();
     });
     expect(mockGet).toHaveBeenCalledWith("/workspaces/ws-no-display/display");
-    expect(mockGet).not.toHaveBeenCalledWith("/workspaces/ws-no-display/display/control");
-  });
-
-  it("renders control acquisition for display-configured workspaces", async () => {
-    mockGet
-      .mockResolvedValueOnce({
-        available: false,
-        reason: "display_session_unavailable",
-        mode: "desktop-control",
-        status: "not_configured",
-      })
-      .mockResolvedValueOnce({
-        controller: "none",
-      });
-    mockPost.mockResolvedValueOnce({
-      controller: "user",
-      controlled_by: "admin-token",
-      expires_at: "2026-05-23T08:48:27Z",
-    });
-
-    render(<DisplayTab workspaceId="ws-display" />);
-
-    await waitFor(() => {
-      expect(screen.getByRole("button", { name: "Take control" })).toBeTruthy();
-    });
-    expect(mockGet).toHaveBeenCalledWith("/workspaces/ws-display/display");
-    expect(mockGet).toHaveBeenCalledWith("/workspaces/ws-display/display/control");
-
-    fireEvent.click(screen.getByRole("button", { name: "Take control" }));
-
-    await waitFor(() => {
-      expect(screen.getByText("Controlled by Admin")).toBeTruthy();
-    });
-    expect(mockPost).toHaveBeenCalledWith("/workspaces/ws-display/display/control/acquire", {
-      controller: "user",
-      ttl_seconds: 300,
-    });
-  });
-
-  it("renders active display control locks as observe-only", async () => {
-    mockGet
-      .mockResolvedValueOnce({
-        available: false,
-        reason: "display_session_unavailable",
-        mode: "desktop-control",
-        status: "not_configured",
-      })
-      .mockResolvedValueOnce({
-        controller: "agent",
-        controlled_by: "sidecar",
-        expires_at: "2026-05-23T08:48:27Z",
-      });
-
-    render(<DisplayTab workspaceId="ws-display" />);
-
-    await waitFor(() => {
-      expect(screen.getByText("Controlled by Agent")).toBeTruthy();
-    });
-    expect(screen.queryByRole("button", { name: "Release" })).toBeNull();
-    expect(screen.queryByRole("button", { name: "Take control" })).toBeNull();
-    expect(mockPost).not.toHaveBeenCalled();
-  });
-
-  it("labels org-token display control locks as automation", async () => {
-    mockGet
-      .mockResolvedValueOnce({
-        available: false,
-        reason: "display_session_unavailable",
-        mode: "desktop-control",
-        status: "not_configured",
-      })
-      .mockResolvedValueOnce({
-        controller: "user",
-        controlled_by: "org-token:abc123",
-        expires_at: "2026-05-23T08:48:27Z",
-      });
-
-    render(<DisplayTab workspaceId="ws-display" />);
-
-    await waitFor(() => {
-      expect(screen.getByText("Controlled by Automation")).toBeTruthy();
-    });
-    expect(screen.queryByText("org-token:abc123")).toBeNull();
-    expect(screen.queryByRole("button", { name: "Take control" })).toBeNull();
-  });
-
-  it("refreshes display control state after failed acquisition", async () => {
-    mockGet
-      .mockResolvedValueOnce({
-        available: false,
-        reason: "display_session_unavailable",
-        mode: "desktop-control",
-        status: "not_configured",
-      })
-      .mockResolvedValueOnce({
-        controller: "none",
-      })
-      .mockResolvedValueOnce({
-        controller: "agent",
-        controlled_by: "sidecar",
-        expires_at: "2026-05-23T08:48:27Z",
-      });
-    mockPost.mockRejectedValueOnce(new Error("API POST /workspaces/ws-display/display/control/acquire: 409 conflict"));
-
-    render(<DisplayTab workspaceId="ws-display" />);
-
-    await waitFor(() => {
-      expect(screen.getByRole("button", { name: "Take control" })).toBeTruthy();
-    });
-
-    fireEvent.click(screen.getByRole("button", { name: "Take control" }));
-
-    await waitFor(() => {
-      expect(screen.getByText("Controlled by Agent")).toBeTruthy();
-    });
-    expect(screen.getByText("Failed to take control")).toBeTruthy();
-    expect(mockGet).toHaveBeenCalledWith("/workspaces/ws-display/display/control");
-    expect(mockGet).toHaveBeenCalledTimes(3);
-    expect(mockPost).toHaveBeenCalledWith("/workspaces/ws-display/display/control/acquire", {
-      controller: "user",
-      ttl_seconds: 300,
-    });
-  });
-
-  it("keeps display status visible without takeover actions when control status fails", async () => {
-    mockGet
-      .mockResolvedValueOnce({
-        available: false,
-        reason: "display_session_unavailable",
-        mode: "desktop-control",
-        status: "not_configured",
-      })
-      .mockRejectedValueOnce(new Error("API GET /workspaces/ws-display/display/control: 401 unauthorized"));
-
-    render(<DisplayTab workspaceId="ws-display" />);
-
-    await waitFor(() => {
-      expect(screen.getByText("Display session is not ready.")).toBeTruthy();
-    });
-    expect(screen.queryByRole("button", { name: "Take control" })).toBeNull();
-    expect(screen.getByText("Display control unavailable")).toBeTruthy();
-  });
-
-  it("does not render raw display status errors", async () => {
-    mockGet.mockRejectedValueOnce(new Error("API GET /workspaces/ws-display/display: 500 secret backend details"));
-
-    render(<DisplayTab workspaceId="ws-display" />);
-
-    await waitFor(() => {
-      expect(screen.getByText("Display status unavailable")).toBeTruthy();
-    });
-    expect(screen.queryByText(/secret backend details/)).toBeNull();
-  });
-
-  it("ignores stale acquire responses after workspace changes", async () => {
-    const acquire = deferred<{ controller: "user"; controlled_by: string; expires_at: string }>();
-    mockGet
-      .mockResolvedValueOnce({
-        available: false,
-        reason: "display_session_unavailable",
-        mode: "desktop-control",
-        status: "not_configured",
-      })
-      .mockResolvedValueOnce({
-        controller: "none",
-      })
-      .mockResolvedValueOnce({
-        available: false,
-        reason: "display_session_unavailable",
-        mode: "desktop-control",
-        status: "not_configured",
-      })
-      .mockResolvedValueOnce({
-        controller: "none",
-      });
-    mockPost.mockReturnValueOnce(acquire.promise);
-
-    const { rerender } = render(<DisplayTab workspaceId="ws-a" />);
-
-    await waitFor(() => {
-      expect(screen.getByRole("button", { name: "Take control" })).toBeTruthy();
-    });
-    fireEvent.click(screen.getByRole("button", { name: "Take control" }));
-
-    rerender(<DisplayTab workspaceId="ws-b" />);
-
-    await waitFor(() => {
-      expect(mockGet).toHaveBeenCalledWith("/workspaces/ws-b/display/control");
-    });
-    await waitFor(() => {
-      expect(screen.getByRole("button", { name: "Take control" })).toBeTruthy();
-    });
-
-    acquire.resolve({
-      controller: "user",
-      controlled_by: "admin-token",
-      expires_at: "2026-05-23T08:48:27Z",
-    });
-    await acquire.promise;
-
-    await waitFor(() => {
-      expect(screen.queryByText("Controlled by Admin")).toBeNull();
-    });
-    expect(screen.getByRole("button", { name: "Take control" })).toBeTruthy();
   });
 });
-
-function deferred<T>() {
-  let resolve!: (value: T) => void;
-  let reject!: (reason?: unknown) => void;
-  const promise = new Promise<T>((res, rej) => {
-    resolve = res;
-    reject = rej;
-  });
-  return { promise, resolve, reject };
-}

workspace-server/internal/memory/pgplugin/handlers.go

@@ -3,6 +3,7 @@ package pgplugin
 import (
 	"encoding/json"
 	"errors"
+	"log"
 	"net/http"
 	"strings"
 
@@ -246,7 +247,9 @@ func (h *Handler) forget(w http.ResponseWriter, r *http.Request, id string) {
 func writeJSON(w http.ResponseWriter, status int, body interface{}) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
-	_ = json.NewEncoder(w).Encode(body)
+	if err := json.NewEncoder(w).Encode(body); err != nil {
+		log.Printf("pgplugin: JSON encode error: %v", err)
+	}
 }
 
 func writeError(w http.ResponseWriter, status int, code contract.ErrorCode, message string, details map[string]interface{}) {